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Introduction

Relative edema volume, computed from T2-based CMR images, has been used to define
the Area-At-Risk in myocardial infarction and in the determination of salvagable myocardium
in patients. Following infarction, edema presents as hyperintense regions in T2-weighted
CMR, however, the literature reports disparate data resulting from delayed imaging
and type of MR acquisition.

Purpose

To investigate the time course and extent of myocardial edema in reperfused myocardial
infarction on the basis of T2 maps and T2-weighted STIR imaging.

Methods

Cardiac MR was used to investigate the development and persistence of edema volume
increases in the acute post-infarct period using both T2-weighted STIR imaging and T2 maps. LAD instrumented canines (n=9) underwent three hours of no-flow ischemia followed
by reperfusion and were studied [using Siemens 1.5 T Espree scanner] at five time
points (before and during ischemia and 2, 5, 7 and 56 days post-reperfusion). Scan
parameters for T2-STIR acquisitions were: TE=64ms, TR=2-3 R-R intervals, resolution=0.9x0.9x8.0mm3. T2 maps were computed from multiple T2-prepared acquisitions with different preparation times (0, 24, and 55 ms) with spatial-resolution
of 1.0x1.0x8.0mm3. Late-enhancement imaging confirmed LAD infarction. Areas of interest were determined
as follows: For T2 maps - region with T2 values greater than 2SD from remote territories; and for T2-STIR images- regions exceeding 2SD of the signal intensity of the remote regions.
Edema volume was computed as highlighted areas multiplied by imaging slice thickness.
Percent volume of edema was computed relative to total myocardial volume. Results
are reported as mean ± SEM for each time point.

Figure 1. Time evolution of edema volume in a canine model of ischemia-reperfusion injury measured
on the basis of changes in T2 and signal intensity on T2-STIR images: Note that the
percent volume of edema measured from T2 maps is generally lower than that from T2
STIR and that the edema volume is variable within the acute period of tissue injury
and resolves to near baseline levels by week 8.

Conclusion

This data indicates that the time following ischemia-reperfusion injury, as well as
the mode of MR interrogation, are critical variables in the determination of Area-at-Risk.